We have cloned the ori regions of Enterobacter aerogenes, Erwinia carotovora, Klebsiella pneumoniae, and Beneckea harveyi. A Sal1 digest of chromosomal DNA from these organisms was ligated to the plasmid pMK2004 also digested with Sal1, then transformed into an E. coli K12 polA1 mutant. The ori region from the above organisms was recovered on plasmids as well as was the polA gene from E. aerogenes and E. carotovora. All of the ori-containing plasmids were highly unstable in cells grown in the absence of selection. The size of ori plus inserts ranged from 6.4 Kb in the case of B. harveyi to 18 Kb for E. aerogenes. The plasmids derived from E. carotovora were the only ori plus plasmids that could be transformed into a polA plus E. coli strain. This may be due to the absence of the uncB gene on the E. carotovora ori plus plasmids, which do carry the asn gene. Genetic and restriction maps of these ori regions have been constructed. We have studied promoters within the origin region of S. typhimurium using a plasmid, pMC489. This plasmid carries a promoter-deficient lac Z (alpha) and a single BamH1 site for detecting promoters in inserted BamH1 or Sau3A fragments. The only BamH1 or Sau3A fragment near or within the ori region of S. typhimurium that contained promoter activity was the 106 bp BamH1 fragment from 0 to -106 and then only in one orientation, so that the direction of transcription initiated within this fragment was away from the origin.